The metal-oxide-semiconductor (MOS) devices have been widely used in integrated circuits for their small sizes, low cost of production, ease of integration, etc. The MOS devices can be made either p-type or n-type semiconductors, and complementary pairs thereof can be used to make switching circuits with very low power consumption. Typically, in a semiconductor structure, MOS devices are disposed in both the high voltage areas and the low voltage areas, and known as high-voltage (HV) MOS devices and low-voltage (LV) MOS devices, respectively. For the operation under various conditions such as different levels of voltages, the MOS devices and the related elements may have different modified structures.